Debt is a moral matter. While most economic activity is concerned with the “is” of how things are (investment, consumption and so forth), debts are always entwined with an “ought” – to repay. In discussing controversial debts–for example government borrowing in the euro zone and the U.S.–the moral question should be addressed directly: should these debts be paid off in full, or is some forgiveness justified?

Aristotle can help frame the argument. The philosopher condemned all lending at interest because money cannot create wealth by itself; a loan is just a way for the lender to take advantage of the borrower. Some proponents of Islamic finance make a similar argument, but it is not quite right. Capitalism has shown that loans can indeed produce wealth. If the lent funds are invested well, enabling the borrower to improve his lot and the world’s, then interest payments are the lender’s just reward for providing the fruitful funds.

But Aristotle’s moral logic remains relevant; his condemnation is appropriate for loans which do not share wealth justly between borrower and lender. Unfair loans should not be made, and where they have been, full repayment only compounds the original injustice.

Libertarians, believers in the right of individual to make their own decisions, have another contribution to the moral discussion. They point out that loans are freely agreed contracts which should be honoured. Both sides should understand the possible consequences of their free choices. Borrowers should repay, even if that requires making sacrifices, and creditors who make bad lending decisions should suffer losses.

In the euro zone, some libertarians (and most Germans) consider the borrowers’ obligations to be paramount. The governments of Greece and the other over-extended nations can and should repay all their agreed debts. The citizens just have to work harder and pay more taxes.